The present invention relates to a circuit for balancing a bridge.
A circuit which employs a resistance change type sensor as a constituting element of a bridge, applies a voltage or current across two ends of the bridge, extracts signals from two central nodes, and determines a voltage difference between the two signals as a sensor output signal is widely used. In general, in order to compensate for an unbalanced state caused by a variation or a change in resistors constituting the bridge, a variable resistor is connected to the bridge.
FIG. 4 shows an example of such a circuit. In FIG. 4, resistance change type sensors RS1 and RS2 are constituting elements of a bridge, voltages V.sub.+ and V.sub.- are applied across two ends of the bridge, signals are extracted from two central nodes, and a voltage difference between the two extracted signals is determined as a sensor output signal a. In order to compensate for an unbalanced state of the bridge, a variable resistor VR1 is connected to the bridge. Reference symbols R1 and R2 denote fixed resistors constituting the bridge.
However, it takes much time to adjust the variable resistor VR1, and the bridge balancing circuit employing the variable resistor is not suitable for mass-production. In addition, if the resistance is changed over time after adjustment, the bridge is unbalanced again.